There is a growing need for devices and methods that can detect biomarkers and other chemical or organic species within a sample. For example, many disease states may be diagnosed or their progression monitored by the detection of one or more biomarkers. For example, a test for prostate cancer may rely on the level of prostate-specific antigen (PSA) present in a sample. In still other contexts, such as biowarfare and biodefense applications, there is a growing need for relatively small, sensitive devices that are able to quickly detect the presence of small quantities of harmful agents within the environment.
Phage-displayed peptide libraries have been investigated as a potential tool that could offer the ability to test or screen for a large number of target molecules. For example, phage-displayed peptide libraries having on the order of 1010 unique members offer the promise of universal biorecognition. Unfortunately, this technology has found only limited application in biosensors. In prior work, detecting molecular recognition between phage and target has focused on a “sandwich assay” scheme involving the detection of phage binding to immobilized target using rather complicated and expensive testing equipment such as quartz crystal microbalances, microelectrode arrays, nanowire field effect transistors, bead-based electrochemical immunoassays, electric DNA chips, and fluoroimmunoassays. Still other techniques have been proposed for the rapid detection of, for example, bacteria using a phagemid electrochemical assay system. Still others have proposed using affinity-selected filamentous bacteriophage that is immobilized to piezoelectric transducers. In this last scheme, specific bacterial binding purportedly results in resonance frequency changes.
There thus is a need for a device and method that avoids the problems associated with prior sandwich-based assays. Such a system should be amenable to miniaturization and have a rapid response time.